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Q:I am interested in coating PVC foam boards with paint. I have heard that vacuum coating is a process that will work for this application. What sort of undertaking might this be if I wanted to do it in house? Also, are you aware of any other methods that could be used to coat this type of substrate? –E.S.

A: There are a few things to consider when determining the best path forward when it comes to selecting the proper application process. I think that the overall aesthetic appearance would be a major factor when you select your application. I will highlight several types of application processes to consider the pros and cons.

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Before any process, I have found it particularly effective to first sand the surface with a range of sandpapers (320-400 grit), as this helps promote better paint adhesion. Once I am done with sanding, I have also found it necessary to clean the surface with IPA (isopropanol) to remove any residual surface treatments. Let’s consider vacuum coatings.

You did not mention the size of the substrate, but as a general rule, vacuum coatings are limited by substrate size. The vacuum coating process uses a hopper filled with the paint material, and the board is extruded through a template/die. The amount of vacuum in this hopper controls how much material is left on the surface. The challenge with this process is that it generally coats both sides, making it difficult to handle the board afterward. Another challenge you may face is that vacuum coating will not apply a perfect level coat to the substrate due to variances in substrate thicknesses, often requiring multiple coats to achieve a uniform coat of paint.

These are a few of the things you’d need to consider if you go the route of vacuum coating. You may be able to overcome some of the handling issues with vacuum coating if the system uses a UV-curable coating. The coating would cure instantly but would require sanding between coats until a level substrate was acquired.

You also asked what other options may be available. First, and again depending on the surface aesthetic requirements, you could look at an automated reciprocating spray line equipped with the proper spray guns and tip sizes. This type of system would enable you to coat one side at a time with conventional waterborne or solvent and UV-curable coatings. It would lay down a more uniform coat with less passes than its vacuum coater counterpart.

Lastly, you should consider looking at an indirect roll coating process. This process is what I have typically used when coating foam-core board paper or PVC-laminated substrate. The process is simple. Fill a reservoir with whatever material you would want to run—solvent or waterborne. This material is then transferred from a supply tube to a doctor roller that would then transfer the proper amount of the paint material to the feed wheel. The roller head can then be adjusted up and down to control the pinch to the foam-core substrate. The main feed wheel that transfers the material is coated to various “shore” or “durometer” hardnesses. Typically for your application, a 40-50-shore wheel is used to perform the process.

Whatever process you select would need to meet your manufacturing requirements for speed and ease, aesthetic qualities benefits and cost.